r-PROCESS IN PROMPT SUPERNOVA EXPLOSIONS REVISITED

We reanalyze r-process nucleosynthesis in the neutron-rich ejecta from a prompt supernova explosion of a low-mass (11 M⊙) progenitor. Although it has not yet been established that a prompt explosion can occur, it is not yet ruled out as a possibility for low-mass supernova progenitors. Moreover, there is mounting evidence that a new r-process site may be required. Hence, we assume that a prompt explosion can occur and make a study of r-process nucleosynthesis in the supernova ejecta. To achieve a prompt explosion we have performed a general relativistic hydrodynamic simulation of adiabatic collapse and bounce using a relativistic nuclear-matter equation of state. The electron fraction Ye during the collapse was fixed at the initial-model value. The size of the inner collapsing core was then large enough to enable a prompt explosion to occur in the hydrodynamical calculation. Adopting the calculated trajectories of promptly ejected material, we explicitly computed the burst of neutronization due to electron captures on free protons in the photodissociated ejecta after the passage of the shock. The thermal and compositional evolution of the resulting neutron-rich ejecta originating from near the surface of proto-neutron star was obtained. These were used in nuclear reaction network calculations to evaluate the products of r-process nucleosynthesis. We find that, unlike earlier studies of nucleosynthesis in prompt supernovae, the amount of r-process material ejected per supernova is quite consistent with observed galactic r-process abundances. Furthermore, the computed r-process abundances are in good agreement with Solar abundances of r-process elements for A> 100. This suggests that prompt supernovae are still a viable r-process site. Such events may be responsible for the abundances of the heaviest r-process nuclei. Numazu College of Technology (NCT), Ooka 3600, Numazu, Shizuoka 410-8501, Japan Department of Astronomy, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan National Astronomical Observatory, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan Institute of Physical and Chemical Research (RIKEN) Hirosawa 2-1, Wako, Saitama 351-0198, Japan Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA The Graduate University for Advanced Studies, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan Institute of Laser Engineering (ILE), Osaka University, Yamadaoka 2-6, Suita, Osaka 565-0871, Japan Department of Physics, Science University of Tokyo, Yamazaki 2641, Noda, Chiba 278-8510, Japan